Capacitance sensing systems can sense electrical signals generated on electrodes that reflect changes in capacitance. Such changes in capacitance can indicate a touch event or the presence of ridges and valleys of a fingerprint. Fingerprint sensing may be used for security and validation applications for a variety of user interface devices, such as mobile handsets, personal computers, and tablets. The use of capacitance sensing for fingerprint detection may allow for a sensor to be placed in the surface of a user interface device with a great degree of configurability. That is, a sensor is not specific to a single location for all devices. Rather, fingerprint sensors may be disposed where convenient to the industrial design and user experience.
Capacitance-based fingerprint sensors work by measuring the capacitance of a capacitive sense element, and looking for a change in capacitance indicating a presence of absence of a fingerprint ridge (or valley). Ridges and valleys at identifiable location on an array may be used to reconstruct the image of the fingerprint for use in enrollment, validation, and security applications. When a fingerprint ridge comes into contact with or is close proximity to a sense element, the capacitance change caused by the fingerprint ridge is detected. The capacitance change of the sense elements can be measured by an electrical circuit. The electrical circuit converts the capacitances of the capacitive sense elements into digital values.